Converging behavioral and neural evidence suggests that numerical representations are spatially organized from left-to-right, the so-called mental number line. When judging parity (odd/even), for example, smaller and larger numbers produce faster left- and right-side responses, respectively (the SNARC effect). Three experiments revealed that this spatial organization of magnitude extends to the representation of emotion. In Experiment 1, participants made parity judgments to numbers (0 to 9) and gender judgments (male/female) to human faces whose expressions varied in happiness. Results showed similar patterns of spatial organization across the two dimensions, with right-side responses becoming increasingly faster as numerosity or happiness increased. Experiment 2 showed that magnitude, not valence, underlies this left-to-right organization, and Experiment 3 provided evidence for the flexibility and specificity of magnitude representation. Together, our findings suggest that people automatically extract information about magnitude, regardless of its instantiation, representing disparate dimensions of experience in common spatial (left-to-right) form. Number appears to be but one example of a more general representational system linking space and dimensions of magnitude.